Manual J Report - Home Energy Pros2015-03-03T20:39:23Zhttp://homeenergypros.lbl.gov/forum/topics/manual-j-report?commentId=6069565%3AComment%3A62546&feed=yes&xn_auth=noA lot of contractors wrongly…tag:homeenergypros.lbl.gov,2012-01-14:6069565:Comment:746462012-01-14T17:44:06.077Ztedkiddhttp://homeenergypros.lbl.gov/profile/tedkidd
A lot of contractors wrongly think multi stage provides justification to oversize. Even if the duct work is designed to handle the extra airflow (usually not) this is unfortunate misorientation. A catastrophic misunderstanding of how to deliver comfort and efficiency.<br></br>
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Oversizing removes the value added of 2 stage units, which is the ability to run without satisfying. Initially this may be counterintuitive, but give it some thought. The biggest advantage is having a system that…
A lot of contractors wrongly think multi stage provides justification to oversize. Even if the duct work is designed to handle the extra airflow (usually not) this is unfortunate misorientation. A catastrophic misunderstanding of how to deliver comfort and efficiency.<br/>
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Oversizing removes the value added of 2 stage units, which is the ability to run without satisfying. Initially this may be counterintuitive, but give it some thought. The biggest advantage is having a system that doesn't shut off when the house is experiencing load. This provides much better latent control and much more even distribution to areas that might otherwise be imbalanced. Multi stage provides this advantage if properly sized. It does not if oversized. <br/>
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If we reorient thinking, explain that hvac doesn't heat or cool, it replaces heat or cool. The best, most efficient, most comfortable way to do this is matching loss. Think about hvac as maintaining temperature rather than "heating up" or "cooling down," and the way people think about how to accomplish home performance changes.<br/>
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If you hear multi stage being used as justification for oversizing, your antenna should go up. Ask whose interests the justifier is concerned about, certainly its not the homeowners. With such a low cooling load…tag:homeenergypros.lbl.gov,2012-01-14:6069565:Comment:746442012-01-14T17:23:23.213ZBob Blanchettehttp://homeenergypros.lbl.gov/profile/BobBlanchette
<p>With such a low cooling load I question if oversized 2 stage units are even worth the investment, you may be better off just getting the smaller single stage units. Consider the outputs of the units at the design temperature, rated tonnage is typically done for 95 degree outside conditions, output decreases as temperature goes up.</p>
<p>Also consider what happens if you do happen to slightly undersize? Your house might be slightly warmer than the thermostat setting on design days for a few…</p>
<p>With such a low cooling load I question if oversized 2 stage units are even worth the investment, you may be better off just getting the smaller single stage units. Consider the outputs of the units at the design temperature, rated tonnage is typically done for 95 degree outside conditions, output decreases as temperature goes up.</p>
<p>Also consider what happens if you do happen to slightly undersize? Your house might be slightly warmer than the thermostat setting on design days for a few hours in the afternoon. This of course will be accompanied by full power AC running so there will be a cool draft blowing from the AC vents which can make a room feel cooler than the number on the thermostat. It's not the end of the world if you are slightly undersized.</p>
<p>Manual J does NOT account for thermal storage in your house, which could very well be enough to get through the peak temps of the day. Have you ever noticed a well insulated building is almost always cooler than the outside on a hot afternoon, even when there is no A/C running? That's thermal storage in action. When you did Manual J did you account for appliance/lighting loads that could simply be turned off when it's hot outside? Are there other Manual J variables that could be altered on the hot afternoon to keep temps down in your house?</p> True about the sizing limitat…tag:homeenergypros.lbl.gov,2011-10-25:6069565:Comment:640392011-10-25T04:13:04.670ZChristopher Cadwellhttp://homeenergypros.lbl.gov/profile/ChristopherCadwell
<p>True about the sizing limitations of the nicer stuff. True about the staging capabilities of the better equipment. Just be sure that the control can handle the staging correctly, and not just turn on 2nd stage after a pitiful 8 minutes of run time. I use a thermostat that has a droop setting - so if the temperature droops out of range, then the second stage comes on then and only then, and resumes low stage when the temperature goes back into range. "Passing gear" if you…</p>
<p>True about the sizing limitations of the nicer stuff. True about the staging capabilities of the better equipment. Just be sure that the control can handle the staging correctly, and not just turn on 2nd stage after a pitiful 8 minutes of run time. I use a thermostat that has a droop setting - so if the temperature droops out of range, then the second stage comes on then and only then, and resumes low stage when the temperature goes back into range. "Passing gear" if you will.</p>
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<p>There is great future for inverter technology. Just a prediction. </p>
<p> </p> Carrier has 2 ton 2 stage hea…tag:homeenergypros.lbl.gov,2011-10-25:6069565:Comment:644442011-10-25T00:37:59.451Ztedkiddhttp://homeenergypros.lbl.gov/profile/tedkidd
<p>Carrier has 2 ton 2 stage heat pumps. Pretty sure Goodman and American Standard do as well. I say <strong>heat pump</strong> because I only recommend, and currently have only sold heat pumps. (Once I started digging into the numbers it became apparent to me I needed to <strong><em>recommend </em></strong>heat pumps. If you can't make the horse drink, that's another story. But you need to show him the drinking hole.) </p>
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<p>When you start selling the high end high efficiency…</p>
<p>Carrier has 2 ton 2 stage heat pumps. Pretty sure Goodman and American Standard do as well. I say <strong>heat pump</strong> because I only recommend, and currently have only sold heat pumps. (Once I started digging into the numbers it became apparent to me I needed to <strong><em>recommend </em></strong>heat pumps. If you can't make the horse drink, that's another story. But you need to show him the drinking hole.) </p>
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<p>When you start selling the high end high efficiency stuff, selling just AC is akin to grand theft, malpractice. Particularly when you get to the higher end equipment the incremental cost is negligible, and energy and comfort benefits start to get really big. Educating the consumer about this opportunity, if it becomes a missed opportunity, takes the onus off of your shoulders.</p>
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<p>Carrier also has a 2 ton inverter driven unit (Greenspeed) that drops to 40%, so that ranges down to below 1 ton. </p> All equipment can be tested f…tag:homeenergypros.lbl.gov,2011-10-24:6069565:Comment:644342011-10-24T22:08:34.245Zdale connerhttp://homeenergypros.lbl.gov/profile/daleconner
All equipment can be tested for capacity once it's installed, testing removes all opinions and produces facts.
All equipment can be tested for capacity once it's installed, testing removes all opinions and produces facts. Isn't that the slip you are l…tag:homeenergypros.lbl.gov,2011-10-24:6069565:Comment:640212011-10-24T15:52:17.873ZBud Pollhttp://homeenergypros.lbl.gov/profile/EverettPoll
<p>Isn't that the slip you are looking for, the loss of credibility. If they can re-calculate with "tight construction" and the recommended total ac needed goes up, then the software is bad or the HVAC contractor is fudging the numbers. Either way the builder should now see that this guy is not capable of giving an honest competent answer. This HVAC guy is no longer concerned about properly sizing this system, but in justifying his position, at all costs.</p>
<p>Bud</p>
<p>Isn't that the slip you are looking for, the loss of credibility. If they can re-calculate with "tight construction" and the recommended total ac needed goes up, then the software is bad or the HVAC contractor is fudging the numbers. Either way the builder should now see that this guy is not capable of giving an honest competent answer. This HVAC guy is no longer concerned about properly sizing this system, but in justifying his position, at all costs.</p>
<p>Bud</p> "redone the MJ with tight con…tag:homeenergypros.lbl.gov,2011-10-24:6069565:Comment:644172011-10-24T15:32:02.574ZChristopher Cadwellhttp://homeenergypros.lbl.gov/profile/ChristopherCadwell
<p>"redone the MJ with tight construction and with results of 2.1 &amp; 2.3 tons. Of course that means they still want to install the 3 &amp; 3 ton unit" </p>
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<p>Ohh yeah. Forgot about that tactic.</p>
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<p>Remind them that per <span style="text-decoration: underline;">Man S you can round down by 5%</span>. So the 2.1 will allow them to install a 2 ton. Haha!</p>
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<p>I haven't had a good debate with a contractor or engineer regarding AC sizing for about a half a year. I…</p>
<p>"redone the MJ with tight construction and with results of 2.1 &amp; 2.3 tons. Of course that means they still want to install the 3 &amp; 3 ton unit" </p>
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<p>Ohh yeah. Forgot about that tactic.</p>
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<p>Remind them that per <span style="text-decoration: underline;">Man S you can round down by 5%</span>. So the 2.1 will allow them to install a 2 ton. Haha!</p>
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<p>I haven't had a good debate with a contractor or engineer regarding AC sizing for about a half a year. I forgot how much it is like playing chess.</p> Thank you all for your commen…tag:homeenergypros.lbl.gov,2011-10-24:6069565:Comment:639172011-10-24T15:00:02.894ZArmando Cobohttp://homeenergypros.lbl.gov/profile/ArmandoCobo
<p>Thank you all for your comments. The HVAC contractor has redone the MJ with tight construction and with results of 2.1 &amp; 2.3 tons. Of course that means they still want to install the 3 &amp; 3 ton units since they are 2-stage units and “oversizing AC units doesn’t matter in 2-stage equipment” theory. I really have taken step back, the builder has all the information on both sides of the issue, I’ve sent him the link to this thread, and now it is up to him what equipments he gets…</p>
<p>Thank you all for your comments. The HVAC contractor has redone the MJ with tight construction and with results of 2.1 &amp; 2.3 tons. Of course that means they still want to install the 3 &amp; 3 ton units since they are 2-stage units and “oversizing AC units doesn’t matter in 2-stage equipment” theory. I really have taken step back, the builder has all the information on both sides of the issue, I’ve sent him the link to this thread, and now it is up to him what equipments he gets installed.</p> If he is pushing on the leaka…tag:homeenergypros.lbl.gov,2011-10-22:6069565:Comment:641052011-10-22T22:20:51.101ZJohn Nicholashttp://homeenergypros.lbl.gov/profile/JohnNicholas
<p>If he is pushing on the leakage point, what is he using for the other inputs? I find lots of high variations in temperature inputs. Also what about the Manual D?</p>
<p>Open cell in a crawl space is not as effective as closed cell. I would question that call. There is more margin for the SPF installer on open cell V closed cell. Some contractors in this area do not install closed cell. So one inch of CC on the crawl wall and 2 inches on the Rim Joist would give you higher R Values then…</p>
<p>If he is pushing on the leakage point, what is he using for the other inputs? I find lots of high variations in temperature inputs. Also what about the Manual D?</p>
<p>Open cell in a crawl space is not as effective as closed cell. I would question that call. There is more margin for the SPF installer on open cell V closed cell. Some contractors in this area do not install closed cell. So one inch of CC on the crawl wall and 2 inches on the Rim Joist would give you higher R Values then the rigid polyiso and OC.</p>
<p>As to the Man J and the leakage inputs; ask the guy doing the Manual J to provide the written requirement from ACCA to use Semi-Leaky -- or -- not leaky.</p> Why doesn't the contractor do…tag:homeenergypros.lbl.gov,2011-10-22:6069565:Comment:642032011-10-22T04:54:43.683ZDavid Parkerhttp://homeenergypros.lbl.gov/profile/DavidParker
Why doesn't the contractor doing the Manual J use the 1ACH50 value or the equivalent cfm50 expected blower door value? I am pretty sure wrightsoft lets you do this. I am sure most other Manual J programs allow you to use the expected (or measured in the case of existing) whole building air leakage value. This should make the labels used for the type of construction and the fireplaces irrelevant- the program will use the whole building air leakage value.
Why doesn't the contractor doing the Manual J use the 1ACH50 value or the equivalent cfm50 expected blower door value? I am pretty sure wrightsoft lets you do this. I am sure most other Manual J programs allow you to use the expected (or measured in the case of existing) whole building air leakage value. This should make the labels used for the type of construction and the fireplaces irrelevant- the program will use the whole building air leakage value.